The concepts of cellular radio are well known, and in fact, all major metropolitan areas in the USA today enjoy cellular radio service. However, there are still vast areas in the USA, and also vast areas in the world that do not yet enjoy cellular radio or any form of radio telephone. The reason for this lack of service lays in the cost factors associated with conventional cellular technology. One of the most expensive elements in a cellular system is the central cellular switch. The central cellular switch controls channel choice, handoffs and connection into the various land line carriers. The centralized concepts associated with cellular radio tend to be very expensive, and not very flexible. Also a system using a central cellular switch requires numerous landline connections from the remote radio base sites (cell sites) to the central cellular switch. Land line connections are required for the desired communications links and also for the various control functions.
An approach for assigning channels in a decentralized system is covered in U.S. Pat. No. 4,965,850, which is incorporated herein by references. The present invention is an improvement over U.S. Pat. No. 4,965,850.
The concept of having radios mounted on numerous telephone poles such that the radios connect into the existing land line network has been well publicized. For example, several articles have appeared in the IEEE by Donald Cox who was at Bellcore, the portion of Bell Labs that went to the regional Bells at the AT&T divestiture, at the time the articles were written. The concept of the telephone pole radio system implies decentralization. The underlying assumption was that the local land line telephone company would take on the responsibilities of the cellular switch. However, a problem of that concept was that the various exchange switches might not have the proper functionality, and additionally, the various exchange switches might be owned by another company such that cooperative efforts would be difficult.
To implement the decentralized approach as described in the telephone pole concept in a common carrier broad service environment including vehicular service, the technology disclosed herein considers the following factors. These factors relate to both technology and the operating environment in which cellular operates and include:
1. Relationship to existing land line carrier
2. Call routing
3. Call hand-off
Firstly, the relationship of the wireless company to the long distance carriers must be considered. If, for example, in a current cellular system, a wireless user in Northbrook, Ill. desires to contact a land line customer in New York, the wireless user in Northbrook will be using at least four different companies to complete the call. One for the airtime in the wireless network, another for the local phone company in Illinois that provides control and communication links from the cellular switch to the Northbrook cell site, a third for the long distance carrier, and fourth is the land line company in New York. Naturally, if it would be possible to easily eliminate the local telephone company from the economic picture, the charges to the final customer will be less.
The second factor considered relates to the call routing.
Previously, there was no easy way for a call to be routed to a central switch without extensive land line charges from the telephone pole unit back to the central switch. Presently, the cellular operator takes responsibility for call routing from its various base sites to his switch. Typically, the local cellular operator rents dedicated land lines from the local phone company. In some instances the local cellular operator installs its own microwave links instead of renting various land lines. When microwave links are installed, they replace the dedicated phone lines. When the call is finally connected to the central cellular switch, the cellular operator can connect the call from its cellular switch directly to a local phone company switch.
In an example of current technology, a wireless user in Zion, Ill. located near the Wisconsin border who desires to contact another land line user in Zion, Ill. will be using the Chicago system that has a cellular switch located west of Chicago. The call must be routed from the wireless cell site in Zion to the Cellular Switch near Chicago, and then back into the land line network through several exchanges (switches) to finally get back north up to Zion, Since Zion is located about 50 miles from the cellular switch, this local call becomes a long distance call.
The third factors relate to handoff control. If a vehicular user in Northbrook moves to a location served by an adjacent cell site, the central cellular switches in operation today would know how to handle the handoff. In a decentralized system, there is a need to be able to control handoff without either a central switch, or a hierarchical system that might delegate handoff control to a local switch.
Consequently, there is a need for a system that would provide decentralized operation, without a large cellular central computer to control the various base sites, and yet such that this system could ultimately connect to the various land line services.
S. Arunkumar and R. S. Panwar in an article entitled “Efficient Broadcast Using Selective Flooding” on page 2060 in the IEEE INFOCOM discuss methods of improving the efficiency of the signaling process in the route establishment procedure. In their article they are referring to a US Army mobile subscriber system wherein nodes and links are in a freeform non-grid pattern. System nodes, transmitter and receiver sites, are connected to other nodes via point to point radio links. As nodes are moved around, different selective point to point links are established.
Although radio links between selected sites can be established by referring to standard topographical maps, propagation charts, and antenna compass directions, such procedures are expensive and not flexible. Also, there is the possibility for human error in propagation calculations, or map reading. At installation time, various antennas have to be pointed in specific directions. Also, if new sites are created or removed, then the entire system must be studied to ascertain the impact of the changes. If buildings have been built that are not on the maps, then selected radio paths will not work as planned. Consequently, there is a need for a system that automatically establishes links based on the real propagation path, as opposed to establishing links based on some maps and calculations.
Preassigned channels for each given link requires careful adjustment and careful installation. In fact, when a given radio site is moved, there is seemingly no easy way to know which channels are being utilized in other places in the system that might have propagation links with other unintended sites. Without this prior knowledge, there is no easy way to guarantee a clear channel at any site. Accordingly, there is considerable value in having the channels automatically established without the possibility of interference between links.
A major practical problem in a mobile (remote) radio telephone system is to insure sufficient bandwidth to handle all of the conversations. With preplanned antennas and channel assignment, there is no flexibility to change around spectrum resources in responses to system load. In contrast, in the inventive system described herein, links are automatically established based on signal strength; channels in route are assigned dynamically based on dynamic signal to interference measurements thereby significantly increasing the call handling capacity of the system.
It is the purpose of this invention to offer a new technical approach for a mobile (remote) radio telephone system base on using radio links to connect various sites into the land line network. This approach will have several advantages over the conventional cellular equipment. Further, as the customer base builds, it will be easy to convert some of the telephone pole sites to conventional “cell” sites with a corresponding reduction in the amount of radio spectrum required to provide service. This invention will provide the possibility for new entrants into the cellular operations to cover wide geographic areas with a very efficient system.